89 buick century 3.3L won't start

a neighbor gave up on this car. it overheated on the highway and always ran rough after that. it stayed in the driveway since march. I drove the car home running rough (missing) and blowing black smoke (lean?) i found the plugs were gas soaked, gapped wrong and one had a cracked insulator (at the wire end). i replaced 2 of the 3 ignition coils. i put in a couple of gallons of fresh gas (the tank was almost empty) i got the car to start and drove it around 10-15 minutes. it ran pretty good except it would die out at a stop, but restarted easily. i parked it for a few hours and when i tried to start it again, it ran rough again and died out as soon as i took my foot off the gas. i pulled the vacuum hose off the fuel regulator, cranked the engine and had no leakage. i got a correct ohm meter reading on all six fuel injectors. i pulled up the fuel rails, cranked the engine and got a fine spray out of all six fuel injectors. i replaced the plug wires. i feel i'm missing something simple or could it be a bad head gasket? anyone have any ideas? if so, include all the detail you can. thanks.

sounds like a bad sensor perhaps MAF. isnt it setting any codes? perhaps a clogged fuel filter. run a pressure test.